Extended range carbon pile rheostat



Jan; 31, 1967 J, ATWOOD 3,302,153

EXTENDED RANGE CARBON PILE RHEOSTAT Filed Nov. 23, 1964 F/6 5 25 2G a INVENTOR.

JESSE R. ATVVOOD A T TO/PNE VS United States Patent 3,302,153 EXTENDED RANGE CARBON PILE RHEOSTAT Jesse R. Atwood, Orinda, Calif., assignor to William M. Brobeclr & Associates, Berkeley, Calif., a corporation of California Filed Nov. 23, 1964, Ser. No. 412,965 9 Claims. (Cl. 338-112) This invention generally relates to carbon pile rheostats and more particularly to one having an extended range beyond the normal limits of conventional rheostats.

In brief, the present invention involves a rheostat construction comprised of a number of resistance plates held in a stacked array by means including a plurality of springs. The springs are disposed between adjacent plates, respectively, and arranged to maintain surface contacts on one edge of each adjacent pair of plates while resiliently separating other edges of said plates. The spacing of the plates and the area of surface contact between plates is then adjusted to vary the resistance of the rheostat.

Although commercial carbon pile rheostats are known, these rheostats normally comprise a number of resistance plates held in full abutting contact. The resistance of such carbon piles is varied by increasing or decreasing the contact pressure between the plates, and where the contact pressure approaches zero the current flow through the pile becomes intermittent. In contrast, the carbon pile rheostat contemplated by the present invention provides a continuous smooth current regulation throughout an extended range. Importantly, the resistance of this rheostat is primarily a function of the contact area between resistance plates and the length of the current path through the plates.

A principal object of the present invention is to provide an extended range carbon pile rheostat comprising a pluality of resistance plates having resilient means disposed intermediate the faces of adjacent plates for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces, the resistance of the rheostat being a function of the contact areas and the spacing between plates.

A second object is to provide a carbon pile rheostat of the kind described wherein the resilient means comprises a plurality of springs disposed between adjacent plates, respectively, said springs being arranged to maintain surface contacts at one edge of each adjacent pair of plates while resiliently separating other edges of said plates.

It is another object to this invention to provide a carbon pile rheostat of the type described wherein the resilient means comprises a plurality of springs disposed between plates in alternating fashion at one of two spaced edges of said plates. The arrangement of the springs in the alternating fashion, as described more particularly herein, provides a current fio'w path that is selectively shortened by reducing the spacing between adjacent plates, thereby decreasing the resistance.

Another object is to provide a carbon pile rheostat of the kind described wherein each resistance plate is formed with recesses for receiving one end of a spring, the resilient means for separating one face of each plate from the adjacent face of another plate comprising a plurality of springs. Each spring is disposed in an aligned pair of plate recesses, and the closed coil length of each spring is less than the combined depth of the recesses in which it is received to allow the near faces of adjacent plates to come into full abutting surface contact.

A still further object of this invention is to provide a carbon pile rheostat of the type described and including means for mounting a plurality of resistance plates in a stacked array, said means comprising a support member ice . center opening in each plate.

A still further object is to provide a carbon pile rheostat of the kind described having means for mounting a plurality of resistance plates in a stacked array while allowing the plates to be adjustably positioned relative to each other to vary the surface contact and the length of current flow.

Other objects of this invention will become apparent in view of the following detailed description and the accompanying drawings:

In the drawings forming a part of this application and in which like parts are identified by like reference numerals throughout the same.

FIG. 1 is a substantially vertical section of a rheostat comprised of a pair of carbon piles constructed in a preferred manner as contemplated by this invention;

FIG. 2 is an enlarged detail of one of the carbon piles shown in FIG. 1;

FIGS. 3 and 4 are diagrammatic views illustrating current flow through a carbon pile as shown under conditions of relatively high and low resistance, respectively; and

FIG. 5 diagrammatically illustrates current flow through the carbon pile of FIG. 1 where the adjacent faces of the carbon plates are held in full abutting surface contact, a condition of minimum resistance through the pile.

Referring to FIG. 1 there is shown an extended range rheostat 10 having a pair of carbon piles 11 and 12, each pile comprising a plurality of resistance plates 13 having helical springs 14 disposed intermediate the faces of adjacent plates, respectively. Springs 14 serve as resilient means for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces.

The resistance plates of each carbon pile are mounted in a stacked array by means which allow the plates to be adjustably positioned to increase or decrease the area of intersurface contact between adjacent plates. For this purpose there is provided a pair of electrically conductive end plates 15, 15 and a pair of electrically conductive pressure plates 16, 16, carbon pile 11 being disposed between end plate 15 and pressure plate 16 with carbon pile 12 located intermediate end plate 15' and pressure plate 16'. The spacing between end plates 15 and 15 is determined by the adjustment of a pair of nuts 19 and 20 threadedly mounted on opposite ends of a bolt 18. Bolt 18 extends through center openings in each plate 13 and in pressure plates 16, 16'. A pair of insulator tubes 21, formed of ceramic material, support plates 13 in coaxial alignment upon bolt 18 while also insulating the plates from the bolt. Utility plates 22 and 23, each made of a suitable insulating material such as Benelex, are employed for mounting end plates 15, 15' in spaced relation, and a pressure block 24 that is axially slidable within an opening of utility plate 23 permits an adjustment to be made in the spacing between nuts 19 and 20. Plate 23 also insulates pressure plate 15' from the nut 20 and a pressure washer 25, and utility plate 22, insulates end plate 15 from nut 19 and a second metal washer 25.

An electrical connection is formed between pressure plate 16 and a bus bar 26 by means of a copper strap 27, the bus bar being mounted to utility plate 22. A similar connection is provided by a copper strap 28 extending between pressure plate 16' and a bus bar 29 mounted to utility plate 23. End plates 15, 15' are connected to cables 30 and 31, respectively.

A pair of arms 32 and 33, pivotally joined on an axis 34, are utilized for positioning pressure plates 16, 16' axially along bolt 18. The upper ends of arms 32 and 33 are formed with contact heads 35 and 36, respectively, and each contact head engages one of a pair of spherical balls 37 and 38, each formed of insulating material mounted on bolt 18. As arms 32 and 33 are spread apart, contact heads 35 and 36 move toward each other, thereby increasing the spacing between resistance plates 13 of each carbon pile and decreasing the areas of intersurface contact.

Referring to FIG. 2, helical springs 14 serve to separate one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces. Moreover, the arrangement of springs 14 is such that a surface contact is maintained on one edge 39 of each pair of adjacent plates while a spring 14, disposed between a given pair of plates and located near an edge 40 spaced from contact edge 39, tends to separate the same adjacent faces. More particularly, springs 14 are located in an alternating arrangement, one spring being disposed near the top edges of two adjacent plates and other springs being disposed near the bottom edges of the same plates but on opposite faces thereof. Such an arrangement of springs 14 establishes a zigzag type of current flow through the carbon plates, the distance of flow through the plates depending on the amount of surface contact between plates.

Springs 14 must be of sufiicient strength to overcome the friction forces between carbon plates 13 and insulator tubes 21. In other words, springs 14 must possess sufiicient energy to separate the carbon plates from each other when and as the spacing between end plates and their respective pressure plates is increased. The spacing between end plates and pressure plates is, of course, controlled by operation of arms 32 and 33, in a manner that is hereafter described.

It will be noted that the faces of each resistance plate 13 are milled to form recesses 13a in which one end of a helical spring 14 is received. The depth of each recess is suflicient to allow complete contact of adjacent carbon plate faces without complete compression of the helical springs. Thus, the combined depth of each pair of aligned complementary recesses is greater than the closed coil length of the spring disposed therein.

In operation, the resistance through each carbon pile increases as pressure plates 16, 16' are allowed to move away from their respective end plates 15, 15 under the bias imposed by springs 14. With the arrangement of resistance plates shown in FIG. 2, where there is a maximum spacing between plates 15 and 16, the area of contact between a given pair of resistance plates is reduced to a line, the length of which may vary depending on the size and shape of each plate. Decreasing the area of contact between resistance plates will, of course, increase the resistance through the carbon pile. In addition, as the contact area between plates decreases there will be a corresponding increase in the length of the current path through the carbon pile, thereby producing an additional increase in resistance.

FIGS. 3-5 of the drawings diagrammatically illustrate the direction and amount of current flow through the carbon piles under various operating conditions. FIG. 3 diagrammatically illustrates current flow through the carbon pile where only one edge of each carbon plate contacts the near edge of an adjacent plate, as shown in FIG. 2; FIG. illustrates current flow where each carbon plate is placed in full abutting surface contact with adjacent carbon plates, as shown in FIG. 1; and FIG. 4 of the drawings represents the current flow that is derived by adjusting the spacing between an end plate and its associated pressure plate as to reduce thearea of contact shown by FIG. 1 but increasing the amount of surface contact illustrated in FIG. 2.

Referring again to FIG. 1,arms 32 and 33 tend to be separated near their bottom ends by the springs 14 of each carbon pile. The separation of these arms, however, is limited and controlled by an operating means comprising a motor 40 having a translating drive mechanism 41 that operates a screw 42 mounted in a support bearing 43. Arm 32 is pivoted at its lower end to a traveling block 44 having a threaded surface engaged with screw 42. The lower end of arm 33 is similarly pivoted to a block 45 supported on a slidable connector member 46 through which screw 42 is driven. A slidable drive is formed between connector member 46 and the rotated arbor 47 of translating device 41 by means of a pin and slot connection, and slide blocks 44 and.45 are guided near their base by a base key 50.

With reference to FIG. 1 it Will be apparent that screw 43 and connector member 46 are free to move in either axial direction relative to their mounting, their position being determined by the balance of forces exerted on contact heads 35 and 36 of arms 32 and 33. The internal spring forces of pile 11 tend to pivot arm 33 counterclockwise relative to pivot axis 34, as shown, thereby holding block 45 in abutting contact with a shoulder of connector member 46. Springs 14 of carbon pile 12 apply a force pivoting arm 32 in a clockwise direction, as shown, the movement of block 44 along screw 43 being restrained by its threaded connection thereto. It will be further evident that rotation of screw 42 will move block 44 axially therealong, selectively increasing or decreasing the spacing between blocks 44 and 45. Spreading arms 32 and 33 allows both carbon piles to expand, thereby reducing the interplate contact area while increasing the length of the current path with the result that the resistance of each pile is increased. Moving arms 32 and 33 toward one another will, of course, produce exactly the opposite effect. The actuating forces applied to pressure plates 16, 16 will be the same since an imbalance would move arms 32, 33, blocks 44, 45, screw 42 and connector 46, as a unit, in the direction of least pressure. Thus, carbon piles 11 and 12 will possess balanced resistances through the full range of adjustment. Although a preferred embodiment of this invention has been illustrated and described, various changes may be resorted to without departing from the spirit of the invention or the scope of the attached claims, and each of such changes is contemplated.

What I claim is:

1. A carbon pile rheostat comprising; a plurality of resistance plates, each plate having two faces on opposite sides thereof, each face being normally in contact with a face of an adjacent plate; resilient means disposed intermediate said plates for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces; and

means for adjustably positioning said plates in relation to each other while maintaining said resilient means under stress.

2. A carbon pile rheostat comprising: a plurality of resistance plates, each plate having two faces on opposite sides thereof, each face being normally in contact with a face of an adjacent plate; a plurality of springs disposed between adjacent plates, respectively, said springs being arranged to maintain surface contacts on one edge of each adjacent pair of plates and to resiliently separate other edges of said plates; and means for adjustably positioning said plates in relation to each other while maintaining said springs under stress.

3. A carbon pile rheostat comprising: a plurality of resistance plates, each plate having two faces on opposite sides thereof, each face being normally in contact with a face of an adjacent plate; resilient means disposed intermediate said plates for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces, said resilient means comprising a plurality of springs disposed between plates in alternating fashion at one of two spaced edges of said plates; and means for adjustably positioning said plates in relation to each while maintaining said springs under stress.

4. A carbon pile rheostat comprising: a plurality of resistance plates, each plate having two faces on opposite sides thereof, each face being normally in contact with a face of an adjacent plate and having a recess formed therein for receiving one end of a spring, the recesses formed on opposite sides of a given plate being located near opposite edges thereof, each resistance plate having its recesses aligned with recesses of adjacent plates; a plurality of helical springs, one spring being disposed in each aligned pair of plate recesses for biasing the near faces of two adjacent plates apart, the closed coil length of each spring being less than the combined depth of the recesses in which it is received to allow the near faces of adjacent plates to come into surface contact; and means for adjustably positioning said plates in relation to each while maintaining said springs under stress.

5. A carbon pile rheostat comprising: a plurality of resistance plates, each plate having two faces on opposite sides thereof and an opening therethrough, each face being normally in contact with a face of an adjacent plate; means for maintaining said plates in a stacked array including an insulator tube extending through the opening of each plate; resilient means disposed intermediate said plates for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces, said resilient means comprising springs respectively disposed between plates in alternating fashion near one of two spaced edges of each plate, the spaced edges of each plate being on substantially opposite sides of said insulator tube; and means for adjustably positioning said plates in relation to each other axially of said insulator tube while maintaining said resilient means under stress.

6. A carbon pile rheostat comprising: a plurality of resistance plates, each plate having two faces on opposite sides thereof, each .face being normally in contact with a face of an adjacent plate and each plate having an opening therethrough; means for mounting said plates in a stacked array comprising an end plate, a pressure plate and an insulator tube, said tube extending through the opening of each resistance plate, said end plate and pressure plate confining said resistance plate therebetween; resilient means disposed intermediate said plates for separating one face of each plate from the adjacent face of another plate while maintaining surface contact between adjacent plate faces; and means for adjustably positioning said pressure plate relative to said end plate while maintaining said resilient means under stress.

7. The carbon pile rheostat of claim 6 wherein said resilient means comprises a plurality of springs disposed intermediate adjacent plates, said springs being arranged therebetween for resiliently separating first portions of adjacent faces and holding other portions in surface contact.

8. The carbon pile rheostat of claim 6 wherein said resilient means comprises a plurality of springs disposed between plates in alternating fashion at one of two spaced edges of said plates, the spaced edges of each plate being on substantially opposite sides of said insulator tube.

9. The carbon pile rheostat of claim 6 wherein the faces of each plate are formed with a recess for receiving one end of a spring, the recesses formed on opposite sides of a given plate being located near opposite edges thereof, one resistance plate having its recesses aligned with recesses of adjacent plates, and further wherein said resilient means comprises a plurality of helical springs, one spring being disposed in each aligned pair of plate recesses for biasing the near faces of two adjacent plates apart, the closed coil length of each spring being less than the combined depth of the recesses in which it is received.

References Cited by the Examiner UNITED STATES PATENTS 1,891,410 12/1932 Greene 338-112 X 1,950,606 3/1934 Gindre 338112 2,026,405 12/1935 Thompson 338-112 2,406,449 8/ 1946 Whittaker 338112 2,797,285 6/1957 Sharik 3381 12 X 2,820,872 1/1958 Carr 338-113 X 3,159,805 12/1964 Bordeaux 33825 X RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner. 

1. A CARBON PILE RHEOSTAT COMPRISING: A PLURALITY OF RESISTANCE PLATES, EACH PLATE HAVING TWO FACES ON OPPOSITE SIDES THEREOF, EACH FACE BEING NORMALLY IN CONTACT WITH A FACE OF AN ADJACENT PLATE; RESILIENT MEANS DISPOSED INTERMEDIATE SAID PLATES FOR SEPARATING ONE FACE OF EACH PLATE FROM THE ADJACENT FACE OF ANOTHER PLATE WHILE MAINTAINING SURFACE CONTACT BETWEEN ADJACENT PLATE FACES; AND MEANS FOR ADJUSTABLY POSITIONING SAID PLATES IN RELATION TO EACH OTHER WHILE MAINTAINING SAID RESILIENT MEANS UNDER STRESS. 